Re: [PATCH 3/3] KVM: make make_all_cpus_request() lockless

From: Avi Kivity
Date: Wed Jan 05 2011 - 04:55:09 EST

On 01/05/2011 11:40 AM, Xiao Guangrong wrote:
Now, we have 'vcpu->guest_mode' to judge whether need to send
ipi to other cpus, this way is very exact, so checking request
bit is needless, then we can drop the spinlock let it's collateral


@@ -147,11 +147,9 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)

zalloc_cpumask_var(&cpus, GFP_ATOMIC);

- raw_spin_lock(&kvm->requests_lock);
- me = smp_processor_id();
+ me = get_cpu();
kvm_for_each_vcpu(i, vcpu, kvm) {
- if (kvm_make_check_request(req, vcpu))
- continue;
+ kvm_make_request(req, vcpu);
cpu = vcpu->cpu;
if (cpus != NULL&& cpu != -1&& cpu != me&&
@@ -163,7 +161,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
smp_call_function_many(cpus, ack_flush, NULL, 1);
called = false;
- raw_spin_unlock(&kvm->requests_lock);
+ put_cpu();
return called;

Maybe we can drop 'cpu != me' and then we don't need to disable preemption?

Can be done in a later patch.

Anyway, I really like this, requests_lock is an ugly wart.

error compiling committee.c: too many arguments to function

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